Eelco, can you please elaborate on what the problem was with JBoss? It
seems that me that if we can dump our cache into the tempdir, that is
the ideal solution. I suspect existing technologies do the same.
Johan, one of the issues we worried about is when these resources are
cleaned up. Is the container responsible for clearing them on
startup/shutdown or does a cleanup occur on a webapp-basis or never at
all?
Thanks,
Gili
--Original Message Text---
*From:* Johan Compagner
*Date:* Tue, 04 Jan 2005 17:07:41 +0100
You can write to disk in a webapplication
Use the work dir:
ServletContext.getAttribute("javax.servlet.context.tempdir");
That will return a File object that points to the work dir for the
current webapplication.
Gili wrote: Ok, so to rehash some points:
1) Currently we parameterize the image URL on the session ID and
parameters used to render the image
2) We write out the image to disk somewhere (although I don't know
where, can you elaborate?)
My personal requirements are:
1) Render image once per page, not per session or view.
2) Do not expose image parameters if possible. Ideally the URL should
read "image<number>.<extension>" and we'll have some lookup table
somewhere that maps image creation parameters to image URLs -> reuse
the same image if the same parameters are used (server-side).
I remember reading about JBoss not giving you write access to
the webapp dir (heck, you could be running inside a JAR). I feel this
problem related to handling links to images in general, not just
dynamically generated ones, if their URL falls under the servlet
context path.
What we could do (solves all problems I know about) is handle
image URLs within the WebApp servlet itself. That is, we never write
the images to disk if they're dynamically generated and "cacheDir"
(some new property I made up) is not set. For JBoss and others cacheDir
will be unset so it'll default to caching in memory. For Tomcat and
others, it'll be set to the default temporary directory for the webapp
so we'll cache to disk. What will happen is that someone will refer to
/MyWebApp/myImage.jpg -- the servlet will recognize that the URL refers
to an image, use the appropriate resource location mechanisms -- and
stream back the image (whether dynamic or static). And ideally we'd
throw in a "image parameters -> image URL" mapping somewhere so we
don't have to expose inner details to the HTTP clients.
My only concern is that for JBoss, dynamically generated images
would be expensive. Still, I don't think we have a choice in such cases
if we absolutely cannot write to any directory. What do you think?
Gili
On Tue, 04 Jan 2005 15:45:50 +0100, Eelco Hillenius wrote:
None yet. We're thinking about it.
Eelco
Gili wrote:
I saw a lot of discussion of the various problems and possible
solutions but none of them was agreed upon because they each had their
own problem. All I know is that in my case the dynamically-generated
images should be treated as cacheable because they will not change with
clicks (i.e. reference count). What is the proposed solution?
Gili
On Tue, 04 Jan 2005 13:03:00 +0100, Eelco Hillenius wrote:
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